The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
The invention relates to phasing of the chain assemblies and the sprockets to modify the impact noise spectrum and chordal action noise spectrum. Specifically, the invention includes the use of timing chains in conjunction with phased sprockets to alter the noise spectra in an engine timing system. The invention also includes the use of random chains in conjunction with phased sprockets to alter the noise spectra.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing devices as well as for the transfer of power from the torque converter to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
Conventional silent chains typically include both guide links and inverted tooth links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act to position the chain laterally on the sprocket. Guide links typically do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links or driving links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the links and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft. The rotation of a camshaft is thus controlled by and dependent on the rotation of the crankshaft through the chain. A chain for an engine timing drive application is shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference.
A conventional chain drive may include a chain assembly of extended width in order to provide a chain of greater strength. Alternatively, two chain assemblies may be placed side-by-side between pairs of sprockets in order to achieve the equivalent power transmission results as a single extended width chain.
Engine timing systems conventionally include at least one driving sprocket located on the crankshaft and at least one driven sprocket located on the camshaft. Rotation of the crankshaft causes rotation of the camshaft through the chain and sprocket system.
The most basic conventional engine timing system typically includes a single sprocket on the crankshaft connected to a single sprocket on the camshaft, with the crankshaft sprocket having one-half the number of teeth of the camshaft sprocket. Such a camshaft typically controls the valve train operation through hydraulic lifters and rocker arms connected to the valve stems.
A more complicated engine timing system of the prior art connects the crankshaft with two overhead camshafts by a pair of chains. The crankshaft includes two sprockets. Each chain is connected to a single sprocket on each of the two overhead camshafts. Typically, the chain systems will include tensioners on the slack side of each chain to maintain chain tension and snubbers on the tight side of each chain to control chain movement during operation.
More complicated engine timing systems are also utilized in the prior art. Such systems include timing systems having two (or dual) overhead camshafts for each bank of cylinders. The dual camshafts on a single bank can both be rotated by connection to the same chain. Alternatively, the second camshaft can be rotated by an additional camshaft-to-camshaft chain drive. The cam-to-cam drive chain can also include single or dual tensioners for chain control. All of these structures are known in various forms in the prior art.
Conventional timing systems of the prior art can also include more complicated structures than a single sprocket on the crankshaft driving a single sprocket on a camshaft. Some systems include an idler sprocket between the crankshaft and camshaft. One chain system drives the idler which in turn drives either single or dual overhead camshafts. The sizing of the idler gear is such as to allow different rotational speeds of the crankshaft and camshaft. For example, the crankshaft may rotate twice the speed of the crankshaft by the sizing of the sprockets for the chain and sprocket drive system.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket at a particular moment or time increment.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. The frequency is related to the number of teeth on the sprocket and the speed of the sprocket. The impact can produce sound having objectionable pure sonic tones.
Another cause of noise in chain drives is the chordal action of the chain and sprockets as the chain is driven about the sprockets. Chordal action occurs as the chain link enters the sprocket from the free chain. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce an objectionable pure sonic tone at the frequency of the chain mesh frequency or a derivative of it.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives of the silent chain variety to minimize the objectionable effects of the pure sonic tones. The present invention relates to those attempts to modify sound patterns by various phasing relationships between the chain assembly and the sprockets. Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass of chain) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket.
Phased chain systems are described in U.S. Pat. No. 5,397,280, which is incorporated herein by reference. The phased chain systems described therein include phasing in engine timing drives.
As part of the phased chain and sprocket assembly, the present invention provides a modified sprocket construction. The modified sprocket is used with the phased chain assemblies to provide the phased chain and sprocket relationship.